1. Field of the Invention
The present invention relates to a range shift control for a manually shifted, range-type compound transmission having a xe2x80x9crepeat-Hxe2x80x9d type shift pattern. In particular, the present invention relates to an automatic override for a manually shifted, range-type transmission having a xe2x80x9crepeat-Hxe2x80x9d type shift control with a manually operated range shift selector which, above certain vehicle speeds, will prevent inadvertent shifts from the highest low range ratio into one or more of the lowest low range ratios.
2. Description of the Related Art
Vehicular compound transmissions of the range type, including the combined splitter-and-range type, are well known in the prior art and may be seen by reference to U.S. Pat. Nos. 4,754,665; 5,370,01 3; 5,737,969 and 5,950,491, the disclosures of which are incorporated herein by reference.
Manually shifted, range-type transmissions typically used either a xe2x80x9cdouble-Hxe2x80x9d type shift pattern wherein range shifting was automatic, or a xe2x80x9crepeat-Hxe2x80x9d type wherein the driver is required to manually operate a range selector, usually a button or switch located on the shift knob assembly. Typical xe2x80x9cdouble-Hxe2x80x9d shift range shift mechanisms may be seen by reference to U.S. Pat. Nos. 5,661,998 and 5,911,787, while typical xe2x80x9crepeat-Hxe2x80x9d shift mechanisms may be seen by reference to U.S. Pat. No. 5,899,121, the disclosures of all of which are incorporated herein by reference. xe2x80x9cRepeat-Hxe2x80x9d type shifters are often used where side-to-side shift lever movement is to be minimized.
Synchronized transmissions and transmissions utilizing enhanced synchronizers, such as boosted synchronizers, self-engaging synchronizers, double or triple cone synchronizers and/or synchronizers activated through various assist mechanisms, are known in the prior art and may be seen by reference to U.S. Pat. Nos. 5,588,516; 5,713,447; 5,738,194 and 5,738,196, the disclosures of which are incorporated herein by reference. While such enhanced synchronizers are effective to reduce the force required to shift a heavy-duty transmission, they also may permit engagement of ratios which are inappropriate for existing vehicle operating conditions.
The prior art also includes devices which will block inappropriate shifts (see U.S. Pat. No. 5,471,893 and WO 99/31409) and which will cause automatic range shifting as a function of vehicle speed (see U.S. Pat. Nos. 5,263,379 and 5,673,592).
The prior art devices were not totally satisfactory, as they were complicated and/or expensive and/or unduly restricted operator selection of ratios.
In accordance with the present invention, the drawbacks of the prior art are minimized or overcome by provision of a range shift control for a range-type, manually shifted transmission having a xe2x80x9crepeat-Hxe2x80x9d type shift pattern, which requires a minimal amount of added components and which will prevent inadvertent selection and engagement of ratios which could result in catastrophic damage to the transmission, but will otherwise allow the driver to select and engage other ratios.
The foregoing is accomplished by sensing the position of the shift lever in the xe2x80x9crepeat-Hxe2x80x9d type shift pattern and, if the operator shifts from the highest ratio position in low range to the lowest ratio position (or ratio positions) in low range, and if vehicle speed exceeds a predetermined reference value (about 15 to 20 MPH), automatically causing a shift to the high range ratio, regardless of the position of the manually operated range selector switch.
Accordingly, it is an object of the present invention to provide a range shift control for a manually shifted, range-type transmission having a xe2x80x9crepeat-Hxe2x80x9d shift mechanism, which will prevent an inadvertent engagement of a potentially catastrophic downshift.
This and other objects and advantages of the present invention will become apparent from a reading of the following description of the preferred embodiment taken in connection with the attached drawings.